Long term hydrothermal effect on the mechanical and thermo-mechanical properties of carbon nanofiber doped epoxy composites

The influence of water absorption on the mechanical and thermo-mechanical behaviour of carbon nanofibre (CNF) doped epoxy composites was investigated. When immersed in seawater for a long interval of 6 months, all the composite specimens endured saturation whilst weight change of composites was periodically monitored after removal of travelling specimens from a water-beaker. The equilibrium water content and the diffusion coefficient of all composites were evaluated with the help of Fick's law of diffusion. The results demonstrated a general reduction in flexural modulus and strength, hardness, storage modulus and glass transition temperature (T-g) for seawater exposed specimens due to absorption of seawater as compared to their unexposed specimens. After-effects of water absorption such as plasticisation, swelling of epoxy polymer, interfacial damages and micro-cracks, were marked as the main reasons behind the deterioration of properties. However, among all, the least degradation in properties was observed in the nanocomposite with 0.75 wt.% CNFs loading. Such trivial degradation in properties is due to formation of strong interface of CNFs with the epoxy polymer. The experimental findings were further confirmed by the microstructures of fractured specimens using field emission scanning electron microscopy.